Japanese Laid-open Patent Publication No. 2005-183649 and U.S. Pat. No. 6,663,442 discuss a multilayer wiring board that has two through holes formed therein side by side and connected together at both end portions or one end portions thereof, thereby removing stub portions of the through holes.
The term “stub” used herein means a branch wire among wires of a printed circuit board or a semiconductor substrate which is neither connected to any terminal (terminated), nor grounded.
According to one method of forming a through hole that connects to an internal layer wire of a printed board, a metal film is formed on the inner wall of a through hole, and is then cut out from the bottom side of the printed board, thereby removing an unnecessary portion to be a stub.
There is a case where pins of a connector or the like are inserted in through holes to mount the connector or the like on a printed circuit board. Because each pin has a tapered tip, some part of the tip portion of the pin does not contact the conductive wall surface of the through hole.
Even if stubs of through holes are reduced by the foregoing scheme of the related art, therefore, stubs are formed at the tip portions of the pins of a connector or the like when the pins are inserted into through holes.
The stubs formed at the tip portions of the pins this way deteriorate the signal transfer characteristic on the board, and particularly, causes significant deterioration of the fast signal transfer characteristic.